sorry for the delay, there is so much new stock arriving at the moment i am like a kid at christmas and keep forgetting to check these questions.
I think you would be happy with either length. I am a bit shorter than you at 6" but 85kg and rode both the 54 and 58 wides on our test. as you would expect the 54 was a bit more playful and great fun to throw about and encoraged me to try spins and stuff off the hits to the side of the pistes. But it was not as stable at speed or as floaty in the powder. so i guess it really depends what kind of riding you like to do. If you are into rails, parks and playing about then go the 154w if speed, carving and the odd bit of jumping and spinning is your bag then the 158 would be perfect. no matter the legth these boards feel llively under your feet and very responsive so i am sure you will love it. I think the Niche Boards are amazing and are the best made boards we stock. If you have any other questions just ping me another message or give the shop a call and ask for Chris. the number is 01603 716655.
Hope this helps